Dienamine-Mediated Asymmetric Inverse-Electron-Demand Hetero-Diels-Alder Reaction of Linear Deconjugated Enones: Diversity-Oriented Synthesis of 3,4-Dihydropyrans

Organocatalytic Diastereodivergent Enantioselective Formal oxa-Diels-Alder Reaction of Unsaturated Ketones with Enoates Under Liquid-Assisted Grinding Conditions

Chiral heterocycles occur in many compounds of interest, but their efficient synthesis is challenging. This study concerns the enantioselective and diastereoselective synthesis of densely substituted chiral pyran derivatives. Diastereodivergence of the oxa-Diels-Alder reaction is achieved by using either a bifunctional amino-thiourea or a monofunctional quinine organocatalyst under ball-milling conditions. Liquid-assisted grinding proves a highly efficient means of affording pyrans in high yield, with high enantiomeric purities and short reaction times.

Organocatalytic Strategies for the Development of the Enantioselective Inverse-electron-demand Hetero-Diels-Alder Reaction

Cycloaddition reactions, in particular Diels-Alder reactions, have attracted a lot of attention from organic chemists since they represent one of the most powerful methodologies for the construction of carbon-carbon bonds. In particular, inverse-electron-demand hetero-Diels-Alder reactions have been an important breakthrough for the synthesis of heterocyclic compounds. Among all their variants, the organocatalytic enantioselective version has been widely explored since the asymmetric construction of diversely functionalized scaffolds under reaction conditions encompassed within the green chemistry field is of great interest. In this review, a profound revision on the latest advances on the organocatalytic asymmetric inverse-electron demand hetero-Diels-Alder reaction is shown.

DBU-Mediated Addition of α-Nitroketones to α-Cyano-enones and α,β-Unsaturated α-Ketoesters: Synthesis of Dihydrofurans and Conjugated Dienes

1,8-Diazabicyclo[5.4.0]undec-7-ene-mediated reactions of α-nitroketones with α-cyano-enones and α,β-unsaturated α-ketoesters have been developed. The products, namely, dihydrofurans and conjugated dienes, were isolated in moderate to good yields, and a range of substitutions were tolerated.

Catalyst-controlled diastereoselectivity reversal in the formation of dihydropyrans

In dihydropyran synthesis, use of (S)-3b is crucial for overcoming the inherent trans-selectivity and obtaining unusual cis-adducts with high enantioselectivity.